The present invention relates to a muffler for use with an engine of an automobile and the like, and more particularly to a muffler of the expansion type, through which engine exhaust gas is passed to damp noise included therein.
Heretofore, a muffler of the expansion type has been used, in which engine exhaust gas is repeatedly expanded and contracted to damp its pulsating noise.
However, not only in the case of this expansion type muffler, but also in the general case, when an outlet pipe is provided for flow of exhaust gas therethrough in contracted state, usually the end of pipe has been cut at right angles to the axis of pipe which increases flow resistance thus increasing back pressure. In addition, Karman's vortex street to cause secondary noise of gas flow, and the like may be generated.
Further, in the usual muffler of the expansion type, there are the disadvantages that when the exhaust gas flows from an inlet pipe into the muffler, the uniform velocity core of the jet which is produced (jet-like portion conically converging as the gas flow leaves the inlet pipe, and having a length which is about five times the diameter of inlet pipe) strikes against the rear end plate of the muffler body and rebounds therefrom to generate a large quantity of noise. Also, when the exhaust gas flows into and expands within the muffler main body, Karman's vortex street and turbulence will occur to cause secondary noise.
The usual muffler of the expansion type has the further disadvantage that except during normal running of the engine, strange noise is produced at the time of quick acceleration and quick deceleration, and even though this disadvantage is eliminated, strange noise maybe produced depending upon the position of the mounting of the engine, as well as for other reasons.
In the usual muffler of the expansion type, when a throttled portion, i.e., a transition from a larger to a smaller diameter is formed at the open end of the exhaust gas inlet pipe, the pressure pulsation of exhaust gas is roughly rectified. However there is fatal drawback for such a muffler in that secondary noise of gas flow will occur as will be described below; such noise must be eliminated.
The muffler according to this invention is made to eliminate above mentioned disadvantages.